1. Field of the Invention
The present invention relates to a positive-working resist composition for use in double layer resist processing.
2. Description of the Related Art
Due to the necessity for treating a large amount of information at a high speed an integrated semiconductor device, which plays a main role in an information treating device, has been developed and large-scale integrated circuits (LSI) and very large-scale integrated circuits (VLSI) are now in practical use.
This integration is carried out by a miniaturization of unit elements and the use of a minimum line spacing of the wiring pattern on an order of submicrons, and further, a multi-layer wiring process is carried out. Therefore, many minute steps are formed on a semiconductor wafer when producing integrated circuits.
When manufacturing a semiconductor integrated circuit, a resist is coated on the semiconductor substrate, and then selectively exposed and developed to dissolve the exposed portions or unexposed portions, and finally, a through hole is formed. Thereafter, a photo-etching technique (photolithography or electron-beam lithography) is conducted, whereby a conductive film or an insulating film is etched by dry-etching.
Therefore, as a process for precisely forming a fine pattern while neglecting the influence of the steps, a multi-layer resist having a double-layer or triple-layer structure has been employed. Especially, a double-layer resist process having fewer process steps is generally employed.
In a double-layer resist process, a novolac resist is coated on a substrate having steps, as a lower-layer resist providing a level surface, followed by coating a upper-layer resist thereon, which resist has an oxygen-plasma resistance and a high resolution.
Many kinds of double-layer resist have been proposed, but an electron-beam resist which can provide a resolution on an order of sub-microns has not been developed.
As a positive resist having a superior oxygen-plasma resistance, a copolymer having the following formula (1) was proposed by the present inventors (see Japanese Application No. 2-61552). ##STR2## wherein, R.sub.1 means CH.sub.3, CF.sub.3, CN, CH.sub.2 OH, or CH.sub.2 CO.sub.2 R, wherein R means an alkyl having 1 to 5 carbon atoms
R.sub.2 means hydrocarbon group having at least one Si, PA1 R.sub.3 means OH, O--C( CH.sub.3).sub.3, NH.sub.2, or NHCH.sub.2 OH, and, a ratio of n to m is more than 0 and is 1 or less than 1. PA1 R.sub.2 means a hydrocarbon radical having at least one Si, PA1 R.sub.3 means OH, O--C(CH.sub.3).sub.3, NH.sub.2 or NHCH.sub.2 OH, and, a ratio of n to m is more than 0 and is 1 or less than 1.
The molecular weight of the copolymer is from 20,000 to 1,500,000.
A cross-linking of this resin at the R.sub.3 position is caused by heating, but since it is necessary to enlarge the ratio of a-substituted acrylate having Si as a copolymer to improve the oxygen-plasma resistance, the cross-linking density becomes too low. Accordingly, the resolution is poor, and thus it is difficult to produce a fine pattern of 0.5 .mu.m or less.
It is difficult to resolve the sub-micron pattern for the resist of the above formula (1).
Therefore, there is a need to improve the resolution to make it possible to produce a 0.5 .mu.m or less pattern.